Transposition and modulation: moving music to a new key

Moving a whole song

To transpose means to move every note of a piece up or down by the same amount. Every note moves the same number of half steps, so the distances between the notes (the intervals) stay exactly the same. The tune keeps its shape; it just starts somewhere else.

The first button plays a short tune in C major. The second plays the same tune moved up four half steps, into E major. In the third, two notes forgot to move, and the tune suddenly sounds like a different song.

• In C majorThe original tune.
• Moved up to E majorEvery note four half steps higher: same tune.
• Two notes left behindTwo notes stayed put, and the tune changes mood.

Why move a song?

The most common reason is the voice. Everyone has a range of notes that are comfortable to sing. If the highest note of a song is too high for you, move the whole song down until it fits. Singers often ask for a different key for exactly this reason.

Musicians sometimes also move a song to a key that is easier to play on their instrument. Either way, the listener hears the same song, only higher or lower.

• Higher (D major)The tune climbs to a high A.
• Lower (A major)The same tune five half steps lower.

Try it: sing along with both buttons. Which version fits your voice better?

How to transpose

First, decide how far to move: count the half steps from the old starting note to the new one, black keys included. Then move every note by that many half steps. Move the chords the same way: moving up two half steps, C becomes D and Am becomes Bm.

The new key has its own key signature, with different sharps or flats. The Circle of fifths lesson shows them all.

Try it: Frère Jacques starts C D E C. Move it up seven half steps and it starts G A B G. Can you play the rest on a keyboard?

Transposing instruments

Some instruments read music that is not written at the pitch you hear. They are called transposing instruments. When a B♭ clarinet player reads a written C, the note that sounds is a B♭, one whole step lower. The real sounding pitch, the one a piano would play, is called concert pitch.

The B♭ clarinet and the B♭ trumpet sound a whole step (a major second) lower than written. The horn in F sounds a perfect fifth lower. The E♭ alto saxophone sounds a major sixth lower, and the B♭ tenor saxophone sounds an octave and a whole step lower. The flute is not a transposing instrument: it sounds what is written.

Why write music this way? A player who plays several instruments of one family can keep the same fingering for the same written note. A saxophonist can switch from alto to tenor and read music the same way, even though the sound comes out lower. The buttons play, with the piano sound, what the same written notes C D E F G sound like on each instrument.

• Written C D E F GConcert pitch: what a piano plays.
• B♭ clarinet or trumpetSounds B♭ C D E♭ F, a whole step lower.
• Horn in FSounds F G A B♭ C, a fifth lower.
• E♭ alto saxophoneSounds E♭ F G A♭ B♭, a major sixth lower.

Why the part is rewritten

If a clarinet player simply played from the piano's music, everything would come out one whole step too low, and the two would clash. So the clarinet's part is written one whole step higher: when the piano plays in C major, the clarinet reads in D major, and the two sound the same notes.

Listen to both. In the first, nobody transposed. In the second, the clarinet part has been rewritten, and the two lines sound as one. (Here both parts use the piano sound.)

• Same sheet: clashThe clarinet line sounds a whole step under the piano.
• Rewritten part: togetherThe part is written in D, so both sound in C.

Modulation: a new home in the middle

Transposing moves the whole song. Modulation is different: the song changes its home key partway through, and the new key becomes home, at least for a while.

A very simple kind is common in pop songs: near the end, the music jumps up one half step or one whole step without any warning, and the tune comes back again in the new key. It is like taking one more stair: the same tune suddenly sounds brighter.

• Staying homeThe tune twice in C major.
• Up a half stepThe second time it jumps to D♭ major.
• Up a whole stepThe second time it jumps to D major.

Try it: next time you hear a song, listen near the end for a moment where everything suddenly lifts a little higher.

Gentle modulations to nearby keys

Many pieces change key more gently, to a key next door. A very common move is to the dominant key, the key on the fifth note (C major to G major). Another is to the relative minor or major, the twin that uses the same sharps or flats (C major to A minor). On the circle of fifths these keys sit side by side.

The trick is a pivot chord, a chord that belongs to both keys. A minor lives in C major and in G major, so the music can step through it into G; then the new note F♯ tells your ear it has arrived. In the second example, F major (in both C major and A minor) leads to E major, whose G♯ points to the new home, A minor.

• C major → G majorThrough A minor and D7 to a new home on G.
• C major → A minorThrough F and E major to a new home on A minor.

Keep exploring

• Circle of fifthsTwelve keys arranged like the hours on a clock. Tap a key to see its sharps and flats, its minor twin and the chords that go with it.
• ScalesA scale is a set of notes climbing step by step, built from a simple recipe. Pick any starting note and hear major, minor, pentatonic, blues and more.
• IntervalsAn interval is the distance between two notes, like counting the stairs between two people on a staircase. Hear every interval and learn how to count it.